/*
 * $Header: /home/jerenkrantz/tmp/commons/commons-convert/cvs/home/cvs/jakarta-commons//httpclient/src/java/org/apache/commons/httpclient/util/ExceptionUtil.java,v 1.5 2004/10/19 18:09:46 olegk Exp $
 * $Revision: 480424 $
 * $Date: 2006-11-29 06:56:49 +0100 (Wed, 29 Nov 2006) $
 *
 * ====================================================================
 *
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */
package org.apache.commons.httpclient.util;

import java.io.InterruptedIOException;
import java.lang.reflect.Method;

import org.apache.commons.logging.Log;

/**
 * The home for utility methods that handle various exception-related tasks.
 * 
 * @author <a href="mailto:oleg@ural.ru">Oleg Kalnichevski</a>
 * @author <a href="mailto:laura@lwerner.org">Laura Werner</a>
 * 
 * @since 3.0
 */
public class ExceptionUtil {

	/** Log object for this class. */
	// private static final Log LOG = LogFactory.getLog(ExceptionUtil.class);

	/**
	 * A reference to Throwable's initCause method, or null if it's not there in
	 * this JVM
	 */
	static private final Method INIT_CAUSE_METHOD = getInitCauseMethod();

	/**
	 * A reference to SocketTimeoutExceptionClass class, or null if it's not
	 * there in this JVM
	 */
	static private final Class SOCKET_TIMEOUT_CLASS = SocketTimeoutExceptionClass();

	/**
	 * Returns a <code>Method<code> allowing access to
	 * {@link Throwable.initCause(Throwable) initCause} method of {@link Throwable},
	 * or <code>null</code> if the method does not exist.
	 * 
	 * @return A <code>Method<code> for <code>Throwable.initCause</code>, or
	 *         <code>null</code> if unavailable.
	 */
	static private Method getInitCauseMethod() {
		try {
			Class[] paramsClasses = new Class[] { Throwable.class };
			return Throwable.class.getMethod("initCause", paramsClasses);
		} catch (NoSuchMethodException e) {
			return null;
		}
	}

	/**
	 * Returns <code>SocketTimeoutExceptionClass<code> or <code>null</code> if
	 * the class does not exist.
	 * 
	 * @return <code>SocketTimeoutExceptionClass<code>, or <code>null</code> if
	 *         unavailable.
	 */
	static private Class SocketTimeoutExceptionClass() {
		try {
			return Class.forName("java.net.SocketTimeoutException");
		} catch (ClassNotFoundException e) {
			return null;
		}
	}

	/**
	 * If we're running on JDK 1.4 or later, initialize the cause for the given
	 * throwable.
	 * 
	 * @param throwable
	 *            The throwable.
	 * @param cause
	 *            The cause of the throwable.
	 */
	public static void initCause(Throwable throwable, Throwable cause) {
		if (INIT_CAUSE_METHOD != null) {
			try {
				INIT_CAUSE_METHOD.invoke(throwable, new Object[] { cause });
			} catch (Exception e) {
				// LOG.warn("Exception invoking Throwable.initCause", e);
			}
		}
	}

	/**
	 * If SocketTimeoutExceptionClass is defined, returns <tt>true</tt> only if
	 * the exception is an instance of SocketTimeoutExceptionClass. If
	 * SocketTimeoutExceptionClass is undefined, always returns <tt>true</tt>.
	 * 
	 * @param e
	 *            an instance of InterruptedIOException class.
	 * 
	 * @return <tt>true</tt> if the exception signals socket timeout,
	 *         <tt>false</tt> otherwise.
	 */
	public static boolean isSocketTimeoutException(
			final InterruptedIOException e) {
		if (SOCKET_TIMEOUT_CLASS != null) {
			return SOCKET_TIMEOUT_CLASS.isInstance(e);
		} else {
			return true;
		}
	}
}
